Because regulation of growth control in eukaryotic cells is intimately connected with regulation of DNA replication, complete understanding of growth control regulation cannot be achieved without understanding regulation of DNA replication. Conversely, understanding the regulation of replication will help define the signaling pathways is proteins encoded by "nuclear oncogenes". The overall objective of our program is to define the elements required for regulating the initiation of DNA replication, from the actions of nuclear oncogene products through the DNA sequence and structures of replication origins. This program consists of 4 projects, each headed by an investigator with different, but complementary, expertise and each focussed on a different, but related, aspect of replication control. Two of the projects involve study of nuclear oncogenes. In one of these projects, the nuclear oncogenes which function to regulate cell growth during different stages of embryonic development will be identified, and the effects of mutation or overexpression of these genes on DNA replication patterns and cell proliferation for replicating one particular nuclear oncogene, the c-myc gene, will be located, the important DNA sequences at this origin will be identified, and proteins which bind to these important sequences will be isolated and tested for biological activity. The other two projects will provide detailed information about aspects of replication origin structure and function. In one of these projects, the essential sequence elements within human DNA sequences which can replace an Epstein-Barr virus (EBV) sequence to generate a functional EBV replication origin will be mapped, proteins which bind to these essential sequences will be isolated, and human genes essential for the function of the EBV- origin-complementing human sequences will be defined. In the other project, the hypothesis that an easily unwound stretch of DNA (DNA Unwinding Element; DUE) is an essential origin component will be tested by detailed sequence and structural analysis of yeast replication origins and the c-myc and EBV replication origins discussed above.